Automatic meter reading (AMR) systems are generally known in the art. Utility companies, for example, use AMR systems to read and monitor customer meters remotely, typically using radio frequency (RF) communications in fixed or mobile implementations. AMR systems are favored by utility companies and others who use them because they increase the efficiency and accuracy of collecting readings and managing customer billing. For example, utilizing an AMR system for the monthly reading of residential gas, electric, or water meters eliminates the need for a utility employee to physically enter each residence or business where a meter is located to transcribe a meter reading by hand.
There are several different ways in which current AMR systems are configured. In a fixed network, endpoint devices at meter locations communicate with readers that collect readings and data using RF communication. There may be multiple fixed intermediate readers, or relays, located throughout a larger geographic area on utility poles, for example, with each endpoint device associated with a particular reader and each reader in turn communicating with a central system. Other fixed systems utilize only one central reader with which all endpoint devices communicate. In a mobile environment, a handheld or otherwise mobile reader with RF communication capabilities is used to collect data from endpoint devices as the mobile reader is moved from place to place.
AMR systems generally include one-way, one-and-a-half-way, or two-way communications capabilities. In a one-way system, an endpoint device periodically turns on, or “bubbles up,” to send data to a receiver. One-and-a-half-way AMR systems include receivers that send wake-up signals to endpoint devices that in turn respond with readings. Two-way systems enable command and control between the endpoint device and a receiver/transmitter.
While conventional fixed networks provide many advantages over manual read meters, they are limited by the power consumption and battery life of the individual meters. Configuring the meters to respond to or initiate communications with a central device is a drain on the battery life of the meters. The meters still require frequent manual servicing to change out batteries, defeating the most significant advantage of a fixed network system.
Battery life can be conserved by programming the meter devices to bubble-up only at particular times or during specific intervals to communicate with a central device. To accomplish this, meter devices include a timing device, clock, or microprocessor-implemented real time clock (RTC) in order to maintain synchronization with the central device and system as a whole and bubble-up or communicate with the system at the desired times.
By way of example, U.S. Pat. No. 4,455,453 relates to remote sensor monitoring, metering, and control. A remote unit includes a central control and processing unit. Clock pulses from a timing network increment real time clock logic within the central control and processing unit. When the real time indication matches the preset desired callback time, the remote unit initiates a telephone call to a central complex. The central complex responds by transmitting back to the remote unit an acknowledgement signal in the form of a synchronization pulse sequence. Upon detection of the synchronization signal, the central control and processing unit effects data transmission. The central complex receives the transmission and analyzes an error code. If the error code is found, the central complex replies with an instruction transmission comprising a leading sync signal, a code indicative of the next desired callback time, and a code indicative of the instantaneous real time for resetting the real time register.
While the system described in U.S. Pat. No. 4,455,453 provides for individual remote unit synchronization, the remote unit will be limited by battery power. Synchronization schemes requiring multiple data exchanges will significantly deplete a battery power source and are thus not generally desirable in battery-powered systems with a plurality of remote units with which to communicate and maintain because of battery and service cost considerations.
A system for periodically communicating data acquired by a remote data unit over a dial-up telephone line to a central computer is disclosed in U.S. Pat. No. 5,239,575. The remote data unit includes a real-time clock that maintains the local time.
U.S. Pat. Nos. 6,351,223 and 6,728,646 also disclose systems that include real time clocks. U.S. Pat. No. 6,351,223, in particular, discloses periodically powering down a microcontroller to ensure a longer life for the battery used in the transmitter.
U.S. Pat. No. 5,994,892, which is directed to an automatic utility meter, includes a real time clock that provides time and date from 1/100th of a second to years. The microcontroller accesses the real time clock at programmable intervals for functions requiring time and date, including time/date to upload data to a central computer.
Using real time clocks within meter devices, however, are a further drain on the battery life of the device because they must operate with a high degree of precision, which in turn requires high current consumption. High-precision RTCs are also relatively high-cost, adding to the overall cost of the individual meter device if included in each device and working against the desired cost-effectiveness of AMR systems.
There is, therefore, a need in the industry for an AMR system that addresses the meter device battery life shortcomings associated with conventional fixed network AMR systems while providing cost-effective meter devices capable of maintaining time synchronization.